The present invention relates to a polyamide resin composition improved in water resistance, oil resistance and, metal halide resistance. More particularly, the present invention relates to a polyamide resin composition which, owing to the addition of an aliphatic carbodiimide compound, is improved in resistance to hydrolysis particularly in an acidic medium of high temperatures, oil resistance and metal halide resistance, as well as to a member made from the above polyamide resin composition, which is useful as an automobile part, an electric or electronic part, a machine part, a living article or an equipment for leisure time amusement, a building material, an industrial material or a packing material.
It has been known that polyamide resins are very stable in an alkaline medium but cause cleavage very easily in an acidic medium owing to acid-induced hydrolysis reaction and radical reaction.
To protect a polyamide resin from hydrolysis, there was proposed addition of an aromatic carbodiimide (see JP-A-6-16933).
In the above addition, however, there has been a drawback in that since the aromatic carbodiimide compound is generally a thermosetting resin, it causes self-crosslinking when it is melt-kneaded with a polyamide resin, lumps of crosslinked material of aromatic carbodiimide are formed in the polyamide resin, making insufficient the kneading.
In the above aromatic carbodiimide compound heretofore used, self-crosslinking is suppressed by introduction of a substituent into the molecule. However, it has been pointed out that since the self-crosslinking is prevented when heated, the decomposition of aromatic carbodiimide is promoted to invite the generation of decomposition gas and the resultant pollution of working environment and, therefore, the aromatic carbodiimide compound is unsuited for practical use.
Meanwhile, as members, used in, for example, automobile engines, wherein water resistance, oil resistance and metal halide resistance are main requirements, metallic members have been used. As such members, there are also used, in a large amount, members containing, as a base material, an aliphatic polyamide resin such as polyamide 6, polyamide 66, polyamide 46. or the like because these members are lightweight as compared with the metallic members and moreover have excellent mechanical properties.
The members containing, as a base material, an aliphatic polyamide resin, however, have had a problem in that when used in a high-temperature oil [for example, an automatic transmission fluid (hereinafter abbreviated to ATF), a brake fluid (hereinafter abbreviated to BF) or a long life coolant (hereinafter abbreviated to LLC)], the members have no sufficient resistance to oil, etc., deteriorate with time, and show significant reduction in strength.
The reason for the deterioration of the aliphatic polyamide resin in the above member is considered to be that when the member is used in, for example, an ATF, the ATF is first oxidized at a high temperature and increases its acidity and, in this acidic atmosphere of high temperature, the aliphatic polyamide resin undergoes thermal oxidation. Further, it cannot be neglected that, in the acidic atmosphere of high temperature, the aliphatic polyamide resin per se undergoes hydrolysis and thereby is deteriorated.
Thus, the upper temperature limit at which the member containing an aliphatic polyamide resin as a base material, used at sites contacting with an ATF is 120 to 130xc2x0 C.; and use of a metallic member is necessary at a temperature range higher than that.
The members containing an aliphatic polyamide resin as a base material have also a problem in that, when they contact with a solution containing a metal halide (e.g. lithium chloride, lithium bromide, lithium iodide, sodium chloride, potassium chloride, magnesium chloride, calcium chloride, barium chloride, zinc chloride, barium iodide, iron chloride, aluminum chloride, nickel chloride or zinc iodide), the metal halide penetrates thereinto from the member surface, generating cracks (generally called stress cracks) on the member surface.
It has been investigated to use, in place of the aliphatic polyamide resin, so-called super-engineering plastics which are lightweight as compared with metallic members, are excellent in mechanical properties and are usable at higher temperatures, such as polyethersulfone (PES), polyphenylene sulfide (PPS), polyetherether ketone (PEEK) and the like. However, many of these super-engineering plastics are inferior in flexibility and expensive as compared with aliphatic polyamide resins; therefore, have found limited applications and are not yet in general practical applications.
In view of the above-mentioned drawbacks of the prior art, the present invention has been made with an aim of providing a polyamide resin composition improved in resistance to hydrolysis particularly in an acidic medium of high temperatures, oil resistance and metal halide resistance.
The present invention also aims at providing a member made from the above polyamide resin composition, applicable even to sites where use of metallic members has been necessary.
In order to achieve the above aims, the present invention provides a polyamide resin composition which comprises a polyamide resin and an aliphatic carbodiimide compound and, owing to the use of the aliphatic carbodiimide compound, is improved in hydrolysis resistance, oil resistance and metal halide resistance; and a member made from the above polyamide resin composition.
The present inventors made an intensive study in order to obtain a polyamide resin composition improved in resistance to hydrolysis particularly in an acidic medium of high temperatures, oil resistance and metal halide resistance. As a result, the present inventors found out that an excellent polyamide resin composition such as mentioned above can be obtained by adding, to a polyamide resin, an aliphatic carbodiimide compound (including a polycarbodiimide compound) having at least one carbodiimide group in the molecule and that a member made from the above polyamide resin composition shows stable mechanical strengths in contact with an ATF, a BF, a LLC or a metal halide. The finding has led to the completion of the present invention.